Warbird Information Exchange

Cracked head nuts are fairly common on the Merlins but if you've never seen one, here are two we pulled off SUSU while we were doing the cams and heads yesterday. We had some oil spooges between the B bank and head so we kinda figured we might find one or two.

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The more I learn about aircraft, the more I realize I still have to learn.

Good info. and pics. I haven't had the privilege of coming across one of those yet, but probably will...

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"They can teach MONKEYS to fly better than that"

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Chris,
What camera/lens did you use for those?
Canso42

I know very little about the Merlin. Where are these nuts located on the engine? Are replacement nuts easy to find? American standard, or British Whitworth thread?

They hold the head to the cylinder bank. BS thread form, I believe. They have to be re-torqued and the valve clearance checked every 25 hours.

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"They can teach MONKEYS to fly better than that"

http://www.heritageflight.org
http://www.bravo369.org

BSF - British Standard Fine - at an educated guess. The same 55° thread angle as Whitworth but finer, strangely enough.

Whitworth, being coarser tended to be used more to get a decent bite into castings etc.

I got a bunch of the cracked ones sitting around as a paperweights.
Rich

Just for those who care, the pictures of the cracked nuts were taken with a Canon SD800 IS. The macro mode works great for detail shots.

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The more I work on them, the more I wonder why!

When you said Merlin nuts I thought you were refering to some of the folks on this board

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Don't touch my junk!!

Cool stuff Chris!

Any chance we could talk you into posting pictures of what you are doing to the plane, the plane itself, things of that nature? SUSU is one of my favorite Mustangs, I'd love to see some shots of the engine work you are doing as well

TC

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"There are two types of people here; airshow whores and airshow prostitutes. The whores, like you and I, do airshow stuff for free, whereas the prostitutes are paid" - Reg Urschler

Do the cracks always seem to start where a thread starts (or ends), or do they seem to crack in a random location?

The Snap-On BS sockets are 12 point rather than 6 pt. I have had a couple crack at a mark made by the socket. I now use a 6 pt socket. The torque on the nuts is in the neighborhood of 100 ft lbs so they do carry a load. I would say it is more of a random thing for location.
Rich

Good conversation goin on guys. I spoke with Big Jim, Jack Rouschs Merlin guy the other day and had a real good conversation with him. I'm more of a round engine guy so needless to say I asked a lot of questions and he took the time to answer them in a very cordial manner. That was much appreciated. I don't know if they tend to crack in a certain spot but on ours, if you look at the pictures closely, you'll notice that both are cracked through the flat where the part number is stamped. weird huh? The torque on the nuts is 115 ft lbs on the intermediates and 100 on the end nuts according to Jim. He also told me that they are trying steel nuts on the heads to alleviate the cracking problem but they do not have faa approval yet. I have Art Vances deal that he wrote up dealing with the day to day operation of the Mustang (I call it "Mustangs for idiots" which I am) and he mentioned that the Rolls and Packard rocker arms were different and he favored one over the other but Jim told me that if you treat the engine nice and preoil religiously, both should be OK. As far as getting some more pictures of SUSU during the annual, I'll leave that up to my trusty sidekick Troy. He's the camera wizard and the guy I trust to follow up my work to make sure everything is good to go. We'll try to shoot a bunch of stuff this weekend and put it on this thread if you want.

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The more I learn about aircraft, the more I realize I still have to learn.

Huh? What are they made of if not steel?

Yes please. One of the most popular areas in vintage aircraft reporting is ~ wait for it ~ getting 'nuts and bolts' details of how restoration, maintainance and operations are carried out. We've had some great threads here on WIX, and I know I'm not alone in wanting to see more.

You'll keep all your 'Merlin nuts' happy that way.

Cheers,

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James K

"Switch on the underwater landing lights"
Emilio Largo, Thunderball.

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